[W126 Coupe] Fouled Spark Plug

[Gerry Van Zandt]

Hi Henry,

Here's a shortened version of Chet's link which is a bit simpler and will redirect you to his URL:

http://bit.ly/cwcUgo

I agree with Chet that this is an advanced intermediate DIY job, to replace the valve guide seals.  It can be done with the cylinder heads on the car.  However, doing just the seals tends to be a band-aid - a temporary fix -- to the real problem which are the valve guides themselves.

Replacing the valve guides requires that the cylinder heads be removed from the car, and be refurbished at a competent machine shop.  A good head refurbishment costs about $500-600 for a machine shop to do, which would include new valve guides and seals being pressed into the heads, and everything cleaned up to look like new, valves/seats ground if needed, springs checked, heads pressure tested for cracks and leaks, etc.  Takes them anywhere from 3-5 days to do this depending on their workload.

I recently did this job of removing the cylinder heads this past spring on my 560SEC.  I used Chet's web page as a partial "Bible" for the job as well as the factory shop manuals. Chet's guide was so helpful it was unbeleiveable!  It took me two full months of working nights and weekends to complete the job. My total time into the job was about 85-90 hours, and then I had about another 10-12 hours of "clean-up" work involved which was mainly fixing minor things like vacuum leaks, etc. However, I was extremely thorough in replacing all soft parts and rubber under the hood, vacuum lines and fittings, motor mounts, fuel lines, intake system rubber, and thermo-vacuum switches, etc.  I also had both the intake and exhaust manifolds ceramic coated for heat reduction purposes (as well as the top of the intake teflon coated for easier cleaning), a process which cost around $300 for everything including cleaning.

I also had to replace one of the cams and to be safe all eight rockers on the passenger side of the engine, as I had a worn cam lobe and rocker due to a lubrication issue -- probably a plugged oiler tube.  This is not uncommon on these cars.  I also had a small head gasket leak on the rear corner which dripped drops of oil onto the exhaust manifold, causing a "burning oiL" smell in the cabin at stoplights. But mostly I was fixing the same problem that you have -- puffs of blue smoke when starting up from a stoplight or when the car was sitting. This is definitely a worn valve guide issue and the only solution is refurbishment/removal of the heads. This problem can happen from around 140-180K miles on these cars, but it always happens no matter what.

To have a competent independent shop do this work, it will run you around $5,000-6,000.  The job is spec'd out for a Benz mechanic at around 25 hours of labor, so at $100 an hour you are looking at (at least) $2,500-3,000 just in labor.  Parts at a minimum will also run you $1,000, but more likely $1,500-2,000 because there is a lot of brittle plastic and rubber in there that will need to be changed if it never has been. The killer for me was an extra $1,000 for a new cam and eight rocker arms.  I had to spend around $300 on special tools, as well.

Things that most definitely will need to be replaced when the heads come off are all rubber vacuum connectors, vacuum lines, idle air distributor hoses and lines (go to the fuel injectors), fuel injector seals and holders, intake and exhaust manifold gaskets, head gaskets, timing chain tensioner and tensioner gasket, very likely the timing chain if it has 100K or more on it, valve cover gaskets, air hoses from the cam covers to the cold start valve and the air cleaner, cold start valve gasket, throttle body gasket, throttle body rubber boot, intake manifold donut rings, and many many more parts.

So, you are looking at a good $5K for a top end job.

If you are interested, here is the list of parts I created for my own rebuild.

http://dl.dropbox.com/u/10675111/SEC_rebuild_parts.pdf

Hope this helps!

Here is some more detailed information on my experience:

http://bit.ly/b9jwHt


Regards,
Gerry



On Sep 3, 2010, at 11:15 AM, mbcoupes-request at mbcoupes.com wrote:


> Message: 3

> Date: Fri, 3 Sep 2010 06:06:37 -0700

> From: "Henry Viveiros" <henryviv at oigp.net>

> Subject: Re: [W126 Coupe] Fouled Spark Plug

> To: "'Mercedes Coupes Mailing Lists'" <mbcoupes at mbcoupes.com>

> Message-ID: <00ef01cb4b68$d7f34f00$87d9ed00$@net>

> Content-Type: text/plain; charset="us-ascii"

> 

> Thanks, Chet, I believe you. Out of curiosity I clicked on the link you sent

> and got this message:

> 

> Sorry, the page you were looking for could not be found.

> 

> Suggested Actions 

> 

> .         Check the URL that you have typed and retry

> 

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